/*
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.facebook.thrift.protocol;

import com.facebook.thrift.TException;

/**
 * <code>TMultiplexedProtocol</code> is a protocol-independent concrete decorator that allows a
 * Thrift client to communicate with a multiplexing Thrift server, by prepending the service name to
 * the function name during function calls.
 *
 * <p>
 *
 * <p>NOTE: THIS IS NOT USED BY SERVERS. On the server, use {@link
 * org.apache.thrift.TMultiplexedProcessor TMultiplexedProcessor} to handle requests from a
 * multiplexing client.
 *
 * <p>
 *
 * <p>This example uses a single socket transport to invoke two services:
 *
 * <p>
 *
 * <blockquote>
 *
 * <code> TSocket transport = new TSocket("localhost", 9090);<br/>
 * transport.open();<br/> <br/> TBinaryProtocol protocol = new TBinaryProtocol(transport);<br/>
 * <br/> TMultiplexedProtocol mp = new TMultiplexedProtocol(protocol, "Calculator");<br/>
 * Calculator.Client service = new Calculator.Client(mp);<br/> <br/> TMultiplexedProtocol mp2 = new
 * TMultiplexedProtocol(protocol, "WeatherReport");<br/> WeatherReport.Client service2 = new
 * WeatherReport.Client(mp2);<br/> <br/> System.out.println(service.add(2,2));<br/>
 * System.out.println(service2.getTemperature());<br/> </code>
 *
 * </blockquote>
 *
 * @see org.apache.thrift.protocol.TProtocolDecorator
 */
public class TMultiplexedProtocol extends TProtocolDecorator {

  /** Used to delimit the service name from the function name */
  public static final String SEPARATOR = ":";

  private final String SERVICE_NAME;

  /**
   * Wrap the specified protocol, allowing it to be used to communicate with a multiplexing server.
   * The <code>serviceName</code> is required as it is prepended to the message header so that the
   * multiplexing server can broker the function call to the proper service.
   *
   * @param protocol Your communication protocol of choice, e.g. <code>TBinaryProtocol</code>.
   * @param serviceName The service name of the service communicating via this protocol.
   */
  public TMultiplexedProtocol(TProtocol protocol, String serviceName) {
    super(protocol);
    SERVICE_NAME = serviceName;
  }

  /**
   * Prepends the service name to the function name, separated by TMultiplexedProtocol.SEPARATOR.
   *
   * @param tMessage The original message.
   * @throws TException Passed through from wrapped <code>TProtocol</code> instance.
   */
  @Override
  public void writeMessageBegin(TMessage tMessage) throws TException {
    if (tMessage.type == TMessageType.CALL || tMessage.type == TMessageType.ONEWAY) {
      super.writeMessageBegin(
          new TMessage(SERVICE_NAME + SEPARATOR + tMessage.name, tMessage.type, tMessage.seqid));
    } else {
      super.writeMessageBegin(tMessage);
    }
  }
}
